1. Field of the Invention
The present invention relates to a liquid-containing type vibration isolating apparatus which is mounted to a vehicle such as an automobile or to general industrial machines so as to absorb vibrations.
2. Description of the Related Art
A liquid-containing type vibration isolating apparatus, which can effectively absorb vibrations of different frequencies in accordance with respective vibrations, has been proposed.
As shown in FIGS. 17 and 18, a rubber main body 126 is disposed between an inner cylinder 112 and an outer cylinder 114 in a liquid-containing type vibration isolating apparatus 110. A liquid chamber is formed within the rubber main body 126.
In tile liquid chamber, a pressure-receiving liquid chamber 130, a second sub-liquid chamber 150 and a first sub-liquid chamber 146 are defined by a partitioning wall member 134 and a second diaphragm 144 so as to be disposed in layers in a radial direction. The pressure-receiving liquid chamber 130 is communicated with the first sub-liquid chamber 146 via a first restricting passage. The pressure-receiving liquid chamber 130 is also communicated with the second sub-liquid chamber 150 via a second restricting passage 120. The sectional area of the second restricting passage 120 is larger than that of the first restricting passage, and the length of the second restricting passage 120 is smaller than that of the first restricting passage. The second diaphragm 144 forms a partitioning wall between the first sub-liquid chamber 146 and the second sub-liquid chamber 150, and serves to expand and contract the second sub-liquid chamber 150. A thin first diaphragm 124 for expanding and contracting the first sub-liquid chamber 146 forms a portion of a partitioning wall of the first sub-liquid chamber 146.
When, for example, shake vibration having a low frequency and large amplitude (e.g., vibration having a frequency of about 5 to 20 Hz and an amplitude of about .+-.0.5 to .+-.1.0 mm) is inputted to the liquid-containing type vibration isolating apparatus 110, the filled liquid flows between the pressure-receiving liquid chamber 130 and the first sub-liquid chamber 146 via the first restricting passage. Liquid-column resonance of the liquid is generated in the first restricting passage, and a damping force (loss factor: tan .delta.) is generated in the liquid-containing type vibration isolating apparatus 110.
Further, when, for example, idle vibration having a relatively high frequency and small amplitude (e.g., vibration having a frequency of about 20 to 50 Hz and an amplitude of about .+-.0.1 to .+-.O.04 mm) is inputted to the liquid-containing type vibration isolating apparatus 110, the first restricting passage becomes clogged, and the filled liquid flows between the pressure-receiving liquid chamber 130 and the second sub-liquid chamber 146 via the second restricting passage 120. Liquid-column resonance of the liquid is generated in the second restricting passage 120, and a dynamic spring constant of the liquid-containing type vibration isolating apparatus 110 is decreased.
In the liquid-containing type vibration isolating apparatus 110, the pressure-receiving liquid chamber 130 and the plurality of sub-liquid chambers 146, 150 are disposed in layers on one side of the vibration isolating apparatus 110 relative to the inner cylinder 112. Because space is limited, the restricting passages which communicate between the pressure-receiving chamber 130 and the sub-liquid chambers 146, 150 must be disposed on the side opposite to these liquid chambers relative to the inner cylinder 112. As a result, the first restricting passage can only be allowed approximately half of tile length of the periphery of the liquid-containing type vibration isolating apparatus 110, viewed from a radial direction thereof. Further, there are limitations as to exerting a large damping force.
Since the pressure-receiving liquid chamber 130 and the plurality of sub-liquid chambers 146, 150 are disposed in layers on one side of the liquid-containing type vibration isolating apparatus 110 relative to the inner cylinder 112, the structure for defining the respective liquid chambers is complicated, and therefore, the number of parts increases.
In the liquid-containing type vibration isolating apparatus 110, the liquid chambers are disposed in layers. The first sub-liquid chamber 146 is formed at the thin first diaphragm 124 provided at the outer cylinder 114 and is able is formed at the thick second diaphragm 144 provided at the partitioning wall member 134, which defines the first sub-liquid chamber 146 and the second sub-liquid chamber, and is able to expand and contract. Vulcanization processes are necessary for a total of three rubber members including the rubber main body 126, the first diaphragm 124 of the outer cylinder 114 and the second diaphragm 144 of the partitioning wall member 134. Accordingly, there are many vulcanization steps, and the vibration isolating apparatus becomes costly.
Since the first-sub liquid chamber 146 and an air chamber 125 for expanding and contracting the first liquid chamber 146 are used for vibration having a low frequency and large amplitude, the first sub-liquid chamber 146 and the air chamber 125 require more space than the second sub-liquid chamber 150. In this type of vibration isolating apparatus, the plurality of liquid chambers are disposed in layers on one side of the apparatus relative to the inner cylinder. Consequently, the space for the first sub-liquid chamber 146 must be small, and a radial direction dimension (thickness) of the first sub-liquid chamber 146 becomes thin. As a result, a diaphragm of the first sub-liquid chamber 146 must be set close to an opposing wall surface or the like. Therefore, if a large load is applied to the vibration isolating apparatus (in a case in which the apparatus is used as an engine mount and the inner cylinder is displaced by a large amount, and for example, in a case in which torque is applied to the liquid-containing type vibration isolating apparatus 110 in a state in which a vehicle is accelerated or decelerated or when an automatic vehicle is stopped while in drive), the first diaphragm 124 may deform by a large amount and contact the opposing surface so as to make vibration difficult. There is a drawback in that adequate vibration reduction (a low dynamic spring constant caused by liquid-column resonance is necessary) cannot be obtained For low-frequency vibration.
In addition, there are cases in which the First diaphragm 124 may contact other vibrating diaphragms when high-frequency vibration is generated. In such cases, it is difficult for a diaphragm for high-frequency vibration to vibrate, and there is a drawback in that adequate vibration reduction (a low dynamic spring constant by the liquid-column resonance is necessary) cannot be obtained for high-frequency vibration. Further, there are cases in which the first diaphragm 124 expands a large amount at the outer cylinder 114 side and is pressed to the inner circumferential surface of the outer cylinder 114 (or a bracket disposed at the outer side of the outer cylinder 114). In this case, it becomes difficult for tile first sub-liquid chamber 146 to expand and contract, and consequently, it becomes difficult for the second sub-liquid chamber 150, which faces the first sub-liquid chamber 146 via the second diaphragm 144, to expand and contract. There is a drawback in that liquid-column resonance in the second restricting passage 120 lessens, and it is difficult for the high-frequency vibration to be absorbed.